Objectives (1) To determine the relationship between male social rank and reproductive success in wild populations of Macaca arctoides; (2) to understand the mechanism(s) of reproductive suppression and its consequences for patterns of genetic transmission in wild groups; (3) to assess the social roles of males of varying rank; (4) to assess the effects of environment and population density on male relationships through comparative analysis of wild and captive populations. ABSTRACT:Previous research with a captive colony of stumptailed macaques established that (1) there is a strong tendency for the alpha male to monopolize breeding (he may sire all infants conceived during his tenure); and (2), overt aggression by the alpha male is an obvious factor in this monopoly. Non-captive populations should be evaluated to assess the generalizability of the result, particularly because of its implications for the susceptibility of stumptails to rapid inbreeding depression. Theoretical evaluation of the "reproductive strategies" of subordinate males suggest the need to document the functional roles that non-breeding' males have in their groups. It is hypothesized that the greater need for male cooperation in group defense in natural environments, and the greater energetic investment required to exclude subordinate males in large, complex areas, may foster inter-male tolerance and possibly sharing of reproductive opportunities in wild stumptailed macaques. We will use a new and unique non-invasive field-sampling system to gather hair samples from all individuals in two wild populations of stumptailed macaques under study. Provisional assessment of maternal geneological relationships within these groups has been made, preparatory to genetic analysis that will assess relatedness and paternity. We will analyze hair samples using PCR-amplification and microsatellite DNA typing. As the few remaining wild populations of stumptailed macaques are becoming isolated due to habitat destruction and fragmentation, thus precluding options for emigration, we will gather information on the adaptability of the species to high densities of males in the group. We will aim to develop means of measuring and maintaining genetic diversity in macaque populations isolated in fragmented habitat. The first available data from wild groups of stumptails on demography, behaviour, parameters of reproductive biology and reproductive seasonality will also be gathered over the next 5 years, for two populations. Key Words reproduction, genetics, social dynamics, paternity, microsatellite DNA, conservation